1. Field of the Invention
The present invention relates to a container useful for storing and feeding liquid, and particularly relates to a variable volume container whose volume changes as a piston member fitted therein moves.
2. Description of Related Art
The variable volume container of this type is employed for example as a container for ink used in stencil printing. In stencil printing machines, ink is supplied to the inner side of a cylindrical printing drum, and the ink is transferred onto a printing sheet through a perforated stencil sheet wound around the outer side of the printing drum. The ink container is normally a cartridge type container detachably mounted to the printing drum, and printing ink is fed from the ink container into the printing drum.
FIG. 15 shows how the ink container 1 is mounted into the printing drum 2. The printing drum 2 is formed to have a cylindrical shape with an ink-permeable circumferential surface which rotates around the central axis of the printing drum. The ink fed into the printing drum 2 from the ink container 1 is pressed toward the outer side of the printing drum 2 by a squeegee roller 3 which rotates as it is in contact with the inner circumferential surface of the printing drum 2. A doctor roller 4 is provided obliquely over and parallel to the squeegee roller 3 with a small gap therebetween, and thereby an ink hold portion P is formed at the valley portion formed between the squeegee roller 3 and the doctor roller 4.
An ink pump 5 is provided in the printing drum 2 to supply printing ink from the ink container 1. The ink pump 5 includes a suction conduit 5a detachably coupled to the outlet 1a of the ink container 1, and an outlet conduit 5b in communication with an ink distribution tube 6 supported parallel to and above the ink hold portion P. Ink sucked and supplied from the ink container 1 using the ink pump 5 is supplied to the ink hold portion P through the outlet conduit 5b and the ink distribution tube 6.
The ink container 1 is formed into a cylinder/piston type container, and the outlet 1a is formed at an end wall 1c that blocks a front end of the cylinder 1b (the right end in FIG. 15). The back end of the cylinder 1b (the left end in FIG. 15) is sealed by a piston member 1d slidably fitted into the cylinder 1b, and thus an ink storage chamber 1e is formed between the end wall 1c and the piston member 1d. The amount of ink contained in the ink storage chamber 1e is reduced as the ink is sucked using the ink pump 5, and as a result the piston member 1d moves toward the front end of the cylinder 1b in the sealed state. The ink container 1 having such a structure is distributed in the market as it has its outlet 1a sealed with a cap 1f as shown in FIG. 16, and when the ink container 1 is used, the outlet 1a removed of the cap 1f is inserted into the suction conduit 5a of the ink pump 5. As shown by the double dotted chain line in FIG. 16, the back end of the cylinder 1b (the upper end in FIG. 16) is provided with a simple cover 7 having an opening, in order to prevent the piston member 1d from coming out.
However, if the ink container 1 is transported or stored in a distribution channel with the cap 1f facing upward, ink could leak from a gap between the piston member 1d and the inner wall of the cylinder 1b, or the piston member 1d could go down by the weight of ink, causing air to enter the ink storage chamber 1e from a gap between the outlet 1a and the cap 1f and mix into the ink. Therefore, the cap side of the container 1 is preferably faced downward as shown in FIG. 16, in other words, the ink container 1 is preferably placed upside down in packing into a box or in display.
As can be seen from FIG. 16, however, the outlet 1a of the ink container 1 is formed to have a diameter smaller than the diameter of the cylinder 1b. As a result, the following disadvantages are encountered if the container 1 is placed with the smaller-sized outlet 1a being faced downward.
(1) This smaller-sized outlet 1a or the cap 1f has to support the entire load of the ink container 1 and the content thereof, and therefore the ink container 1 becomes unstable, and can be easily turned over even by slight vibration.
(2) At the time of packaging, transporting and unloading, if the container 1 is impacted or dropped, impact force could be concentrated at the outlet 1a, causing damage to the outlet 1a and thereby causing leakage of ink from the cylinder 1b. 
In recent years, in order to increase the storage amount of ink, there is a demand that diameter of the cylinder 1b is enlarged as far as the cylinder 1b is accommodated in an attachment space of the printing drum 2. In this case, the outlet 1a would be even smaller as compared to the enlarged cylinder 1b, which makes the disadvantages even more serious.
Furthermore, stencil printing inks recently tend to be lowered in viscosity in order to improve drying and reduce loads on printing machines upon printing. In this case, the diameter of the outlet 1a should be kept smaller in order to prevent inks from flowing out of the container 1 when it is fitted in or removed from the suction conduit 5a. However, this also makes the above-mentioned disadvantages more serious.
It is an object of the present invention to provide a variable volume container which has an improved structure in the vicinity of the outlet and is capable of stably holding the outlet facing downward even if the cylinder of the container is enlarged in diameter.
It is another object of the present invention to provide a container which has an improved structure in the vicinity of the outlet so that the outlet is protected against impact force.